. ABSTRACT As all Center components will use genetically engineered mice, a central Animal Breeding Core (AB-Core) will be used to meet the animal needs of all Center Projects and Pilots and provide cost-effective, uniformly bred and monitored use of CSORDA animals. Additionally, the Core is a resource, particularly for mice which are mutant in opioid-genes, for providing animals for Pilots and research outside of CSORDA at UCLA, as well as many other institutions. The AB-Core was established in 2006 and developed a set of standardized procedures to accomplish this goal. The functions of the AB-Core are as follows: 1. The AB-Core will coordinate with each Project, Pilot and the TA-Core to provide the required cohorts of male and female mice as needed. Planning, prioritization and sharing of animal breeding will be an agenda item at Steering Committee meetings. 2. The AB-Core will maintain each line under optimal breeding management practices. 3. Since multiple CSORDA research components utilize cross-bred lines, the AB-Core will ensure all lines are correctly maintained as congenic on the C57BL/6J background. 4. The AB-Core will follow the correct breeding strategies to ensure wild-type and mutant mice are bred as littermates. 5. The AB-Core will verify that correct patterns of expression are achieved following cre-mediated deletion in both males and females. 6. The AB-Core will coordinate mouse sharing, with a major role of the transfer of breeding pairs between CSORDA performance sites at UCLA and Dr. Kieffer at the Douglas Institute in Montreal.